a. Field of Invention
The invention relates generally to the manufacture of automotive components, and more particularly to a method of weakening a single layer injection molded instrument panel for a Passenger Side Inflatable Restraint (PSIR) hidden door seam, without the seam having characteristic burrs, generally present due to known milling weakening methods.
b. Description of Related Art
When milling soft single layer injection molded instrument panels (primarily of Thermoplastic Polyolefin but also including any blended Poly Propylene material, hereafter referred to as “plastic”) in order to weaken the panel for the Passenger Side Inflatable Restraint (PSIR) hidden door seam, the instrument panel PSIR seam may be milled using a milling cutter, as is known in the art. As illustrated in FIG. 1, conventional milling techniques however can produce burrs 4 along the milled surface 6 of the plastic panel 8. These burrs are objectionable, primarily for reasons of eye safety, in that, during passenger air bag deployment, the burrs may become a source of flying projectiles.
The primary reason for the burrs is due to the lack of surface support for the plastic during milling as the milling cutter's edge passes. The plastic near the surface (on the side being milled) flexes due to the lack of supporting material above it, thus preventing the complete cutting of this surface material. The partially uncut surface material may thus include the burrs described above, which are undesirable for the reasons noted above.
For example, U.S. Publication No. 20030184063 discloses a portion of an instrument panel cover (40) around the fracture-opening section (46) (hereinafter referred to as an “opening surrounding portion”) that is welded to the reinforcement edge portions (45b) and (45c) of the frame member (45). The opening surrounding portion is prevented from following the opening displacement of the fracture-opening section (46), so that when air bag (43) inflates, the fracture-opening section (46) quickly fractures along fracture grooves (40c) into fracture-opening subsections (46a) and (46b). Therefore, the fracture surfaces (peripheral end surfaces) of the fracture-opening subsections (46a) and (46b) are prevented from having sharp edges or burrs.
JP 03110112 teaches that in order to prevent the creeping of a burr to the rear of a core, and to improve workability by forming a recess to the opening-section corresponding section of the core of a top force, a core (10) for an instrument panel is injection molded from a comparatively hard synthetic resin, and sealing materials (15a-15d) consisting of an air-permeable foaming material are covered in conformity with the shapes of various opening sections such as (11a-11g). The core (10) is set to a top force (22), to which recesses (25) are shaped in response to the core opening sections (11), and a skin (19) to a bottom force (21), and a foaming resin material (30) is introduced into cavities (23) and foam-molded. Residual air and a foamed gas are forced to escape through the sealing materials (15) by cubic expansion, and one part (30A) of the materials flow into the sealing materials (15A) by blowing pressure. The permeation of the sealing materials (15A) of the foaming material and the generation of burrs from the opening sections (11) are prevented by bulging into the recesses (25) and the rise of internal pressure with the bulging.
Further, European Patent Application No. 1388467, European Patent No. 893224, U.S. Pat. No. 6,312,633 and UK Patent Application No. 0758242 disclose other methods for preventing or minimizing burrs in PSIR weakening seams.
As readily evident, while the above-identified Patents and Publications disclose methods for minimizing burrs, the methods nonetheless are clearly complex and thus expensive to implement.
It would therefore be of benefit to provide an economical and efficient method of milling a plastic instrument panel for a PSIR hidden door seam, with the milling resulting in a clean cut surface having virtually no burrs along the edges of the milled surface.